1. Field of the Invention
The present invention relates to a moving vehicle system. In particular, the present invention relates to a technique of making an in-position determination, i.e., determining whether a moving vehicle can stop within an allowable range or not.
2. Description of the Related Art
In moving vehicles having multiple axes including a first axis and a second axis, the second axis is often operated based on a condition that the first axis enters a predetermined range (in-position range). For example, in the case of overhead traveling vehicles, when a position in a traveling direction enters a predetermined range, elevation of an elevation frame or lateral feeding is started. In the case of stacker cranes, automated transportation vehicles or the like, when the position in the traveling direction (and the position in the elevation direction of the stacker crane) enters a predetermined range, a transfer apparatus such as a slide fork is operated. Further, in the case of working machines or the like, when the position in the x-direction or the position in the x-y plane enters a predetermined range, a machining tool is moved along the z-direction of the second axis to start machining.
For the sequential operation of the first axis and the second axis, in-position determination has been adopted. In the in-position determination, when the position of the first axis enters an in-position range, operation of the second axis is started. For example, according to the disclosure of JP2000-231412A, subsequent to the movement in the x-y plane, for movement in the z-direction, in-position determination regarding the synthesized moving direction in the x-y plane is made, and one-dimensional in-position determination is made for the two-dimensional movement.
However, in the case of only adopting determination as to whether the current position is within an in-position range or not, after it is determined that the current position is within the in-position range, the moving vehicle may move out of the in-position range due to overshoot. This situation will be described with reference to FIGS. 6 and 7. FIG. 6 shows a situation where the moving vehicle stops without any vibrations. FIG. 7 shows a situation where overshoot occurs due to vibrations of the moving vehicle. In FIGS. 6 and 7, a graph a) shows a trajectory of a position, a graph b) shows a trajectory on a phase plane of the velocity and position, and a graph c) shows determination results of two-stage (rough and fine) in-position determination. In FIG. 6, the moving vehicle is decelerated toward a target position without any vibrations, and no overshoot occurs. In contrast, in FIG. 7, the position and velocity are not stable. The trajectory in the phase plane has a spiral pattern. After making an in-position determination, it becomes necessary to cancel the determination in the middle of operation.